Aluminum bronze alloy containing manganese and chromium and having improved wear resistance



Unite ALUMINUM BRONZE ALLOY CONTAINING MAN- GANESE AND CHROMIUM AND HAVING IM- PROVED WEAR RESISTANCE This invention relates to an aluminum bronze alloy and more particularly to an aluminum bronze alloy having improved toughness and wear resistance.

Aluminum bronze alloys have for years been used as dies for forming and drawing operations for a large group of sheet and plate alloys, such as stainless steel, aluminum, nickel, titanium, mild steel and some copper base alloys. Aluminum bronze alloys used in die applications possess the properties of good corrosion resistance, wear resistance and non-galling against many wrought materials.

The aluminum bronze alloys which in the past have shown the optimum properties for deep drawing dies are those that contain approximately 14% aluminum, a small amount of iron and the balance copper. An alloy of this type has good corrosion resistance and non-galling properties. However, under heavy use in die applications, it wears undesirably fast so that close dimensional tolerances cannot be maintained because of the wear that occurs on the die surface.

The present invention is directed to an aluminum bronze alloy which has the corrosion resistance and the non-galling properties characteristic of aluminum bronze alloys but has greatly improved wear resistance and toughness.

The aluminum bronze alloy of the invention has high uniform hardness, good toughness and excellent wear resistance. This is accomplished by the addition of small amounts of manganese and chromium to the alloy which substantially reduces the tendency of the alloy to form the eutectoid. The addition of manganese and chromium also makes the alloy more homogeneous in the distribution of the metallurgical phases and compounds during solidification and heat treatment and also promotes uniform controlled grain size.

Furthermore, the alloy at the lower end of the chromium range has a finer particle size than the ordinary aluminum bronze alloys which results in better machinability.

The alloy of the invention has the following general composition by weight:

Percent Aluminum 13.0-20.0 Iron 1.0- 8.0 Manganese 1.0 8.0 Chromium 0.5- 3.0 Copper Balance Sttes Patent Percent Aluminum 15.00 Iron 4.25 Manganese 2.00 Chromium 1.50 Copper 77.25

The alloy can be cast either statically or centrifugally to produce a fine grained tough structure having, in the centrifugal cast state, a tensile strength of 90,000 p.s.i., a yield strength of 75,000 p.s.i., an elongation in two inches of 1.5% and a Rockwell C hardness of 40.

The alloy of the invention has greatly improved wear resistance over that of an ordinary aluminum bronze alloy and this increase in wear resistance is most significant since the hardness of the alloy is substantially the same as the hardness of an aluminum bronze alloy having similar proportions of aluminum and iron but not containing the manganese and chromium. This unexpected increase in wear resistance without an increase in hardness is believed to be due to the formation of an intermetallic compound formed predominately of iron and containing chromium, manganese, aluminum and copper. This intermetallic compound is hard and extremely resistant to wear and due to the presence of chromium, provides the alloy with stainless properties which are extremely valuable when employing the alloy as a deep drawing die and using corrosive lubricants.

The metallographic structure of the alloy consists essentially of gamma two phase which is uniformly distributed in a matrix of beta. An intermetallic compound composed of iron, aluminum, copper, manganese and chromium exists in small particles of uniform size and shape. Because of the method of casting and the inoculant used, the intermetallic compound is uniformly distributed throughout the cast section.

In order to obtain optimum properties, the metals used for the alloy should be of high quality. Electrolytic or wrought fire refined copper, high purity aluminum, low carbon iron and high purity manganese and chromium are preferred to be used. It has also been found that the best method of obtaining the desired uniformity in the alloy is by using a double melting procedure whereby a pre-alloy is made. The most satisfactory pre-alloy is one that has approximately 60% aluminum, 8% copper, 20% iron, 5% chromium and 7% manganese.

The melting procedure employed in making the prealloy is such that some copper, along with the iron, chromium and manganese, is placed into the crucible and melting begun. When the copper starts to melt, the iron and other additives are slowly dissolved into the copper during that period when aluminum is added to form an exothermic reaction which helps to dissolve the higher melting point manganese and chromium additions. This pre-alloy is then cast into ingot form and is ready to use for the final alloy.

The final alloy is made by intermixing a predetermined percentage of the pre-alloy and copper. A deoxidizer is added to this alloy in the molten state in the furnace to purge the metal of oxides and soluble gases. These deoxidizers can include the compounds of boron, phosphorus, magnesium and lithium. Deoxidizers of the gas type can also be used. This can include volatile chlorides or any of the inert gases. The dry type deoxidizers are added in quantities of approximately 4 ounces per pounds of metal, and the gas type deoxidizers are passed either through or over the molten metal for a period of five minutes. particular importance because of their abrasive and adverse efiect on the wear resistant properties of the alloy.

Alternatively, instead of employing a pre-alloy, the chromium and manganese can be added directly to a molten aluminum-iron-copper alloy.

Removal of the oxide particles is of To establish complete uniformity of the microstructure and hardness, the alloy is heat treated at an elevated temperature in the temperature range of 1050 F. to 1400 F., such as about 1150 F. Small castings of simple shapes of this alloy can be placed directly into the heat treating furnace at temperature. Large massive castings or intricate shapes are preheated in the furnace at about 400 F. until the section reaches uniform temperature and then are heated directly to the elevated temperature. The castings are held at a temperature in the range of 1050 F. to 1400 F. for one hour plus one-half hour per inch of section thickness greater than one inch, up to a maximum of two and one-half hours at temperature.

After the required soaking time at the elevated temperature, the alloy is cooled at a rate faster than about 20 F. per hour per one inch of section thickness. This rate is conveniently obtained by fan air cooling.

'The alloy can be used to produce articles for wear resistant applications in drawing and forming operations. The articles may take the form of deep drawing dies, holddown dies, wear guides, forming rolls, skids, slides, etc.

The alloy can also be extruded into weldrods or weld wire. The alloy in the form of coated or uncoated weldrod can be overlaid on a metal base by metal spraying or other welding methods, such as heliarc,.metal arc, carbon arc, etc., to obtain a corrosion resistant Wear surface.

It has been found that the addition of manganese and chromium to the copper-aluminum-iron alloys to be used as die materials improves the toughness, wear resistance and corrosion resistance of the alloy and substantially reduces the tendency for eutectoid embrittlernent. As the alloy of the invention will not form the embrittling eutectoid structure to any great extent, more alloying elements can be incorporated in the alloy for a given hardness to thereby obtain increased wear resistance.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. An aluminum bronze alloy, consisting essentially of 13.0% to 20.0% aluminum, from 1.0% to 8.0% iron, from 1.0% to 8.0% manganese, from 0.5% to 3.0% chromium and the balance being substantially copper, said alloy being characterized by having excellent corrosion resistance and having improved toughness and wear resistance.

2. An aluminum bronze alloy having improved wear resistance, toughness and machinability, consisting essentially of from 13.0% to 20.0% aluminum, 1.0% to 8.0% iron, 1.0% to 8.0% manganese, 0.5% to 3.0% chromium and the balance substantially copper, said alloy being characterizedby a tensile strength in the range of 70,000 to 100,000 p.s.i., a yield strength in the range of 65,000 to 80,000 p.s.i., an elongation in two inches of up to 3.0%, and a hardness in the range of 22 to Rockwell C.

3. An aluminum bronze alloy having improved toughness and wear resistance, consisting essentially of 15.00% aluminum, 4.25% iron, 2.00% manganese, 1.50% chromium and 77.25% copper.

4. A drawing die characterized by having excellent corrosion resistance, a hardness in the range of 22 to 50 Rockwell C and improved wear resistance, said die being fabricated from an aluminum bronze alloy consisting essentially of 13% to 20% aluminum, from 1% to 8% iron, from 1.0% to 8.0% manganese, from 0.5% to 3% chromium, and the balance being substantially copper.

5. An aluminum bronze welding electrode consisting essentially of 13% to 20%" aluminum, from 1% to 8% iron, from 1.0% to 8.0% manganese, from 0.5% to 3.0% chromium, and the balance being substantially copper.

References Cited in the file of-this patent UNITED STATES PATENTS Sendzimir Apr. 29, 1958 

1. AN ALUMINUM BRONZE ALLOY, CONSISTING ESSENTIALLY OF 13.0% TO 20.0% ALUMINUM, FROM 1.0% TO 8.0% IRON, FROM 1.0% TO 8.0% MANGANESE, FROM 0.5% TO 3.0% CHROMIUM AND THE BALANCE BEING SUBSTANTIALLY COPPER, SAID ALLOY BEING CHARACTERIZED BY HAVING EXCELLENT CORROSION RESISTANCE AND HAVING IMPROVED TOUGHNESS AND WEAR RESISTANCE. 